This implements `path_filestat_set_times` which is the last remaining filesystem function in wasi we formerly stubbed.
Other minor changes:
* this removes all places we import alias path as pathutil, introducing a utility function `joinPath` where that was used to reduce name conflicts.
* this fixes places where we used different variable names for the same parameter between main and test source.
Signed-off-by: Adrian Cole <adrian@tetrate.io>
41ef17c5c2